1. Field of the Invention
The present invention relates to an optical apparatus, and more particularly to an optical apparatus capable of stably performing a high-speed lens drive.
2. Description of the Related Art
As a technology of moving a lens with high speed and low noise to perform a focusing, as disclosed in Japanese Patent Laid-open No. 5-066336, a technology where a permanent magnet is arranged at a lens side and a coil is arranged at a fixed portion side to drive the lens by direct driving has been known. In this technology, the lens is guided by a guide axis along an optical axis and a lens frame slides on the guide axis to perform lens driving in an optical axis direction.
However, in such a structure, due to a sliding friction on the guide axis, a high-speed lens driving can not be performed. Further, there is a problem that a sliding noise is generated by the sliding friction, or the like.
As a lens driving method for performing a high-speed focusing in order to solve the problem, as disclosed in Japanese Patent Laid-open No. 7-248522, a proposal in which a lens is electromagnetically levitated to electromagnetically drive the lens in an optical axis direction has been made.
An optical apparatus disclosed in Japanese Patent Laid-open No. 7-248522 performs lens driving without providing a sliding portion. Therefore, a high-speed focusing can be performed.
However, since the lens of this optical apparatus is floated and supported by an electromagnetic force, the tilt of the lens with respect to an optical axis is unstable at a lens position other than a position where a coil finally contacts a magnet in an optical axis direction. For example, the tilt of the lens may be changed in accordance with the change of the gravity depending on the attitude of a camera. Further, there is a possibility that the lens is tilted by a behavior of the lens during a focusing operation.
In an optical apparatus of using a TV-AF method (contrast detecting method), as a method for detecting a front focus and a rear focus of an object, a method called wobbling is used. In the wobbling method, a lens is vibrated at high frequency in an optical axis direction to evaluate an image obtained at each position to determine whether or not it is the front focus or the rear focus based on a focusing state of each image. In this case, because the lens vibrates with high speed, the lens is easily tilted in accordance with the vibration mode and there is a possibility that a false image evaluation may be performed.